Energy scavengers, also sometimes known as energy harvesters are increasingly used in electronic systems to reduce the strain on main power sources or, in some cases, to act as main sources of power.
An energy scavenger is a device which converts ambient energy, which would otherwise be wasted, into energy which can be used for a specific purpose. Energy scavengers may be used in a wide variety of applications ranging from indirectly powering emergency telecommunication equipment to powering microelectronic sensors.
A system for indirectly powering telecommunication devices could, for example, comprise a solar panel which would help charge a battery connected to a stationary emergency wireless telephone box located on the side of a remote motorway. Unfortunately, solar power is not always ideal for powering microelectronic circuits in that, often, these circuits are found in relatively dark places.
However, many micro electronic devices, such as acceleration sensors or passive sensors are constantly being exposed to kinetic forces. Consequently, kinetic energy scavengers have been developed to harness a part of the residual ambient energy caused by the acceleration, vibration or dynamic compression of a device.
Kinetic energy scavengers may harness vibratory energy using piezoelectric devices, thereby converting strain in a material into electrical impulses. These devices can be used in a wide variety of applications.
Most energy scavengers comprise multiple interconnected parts which are assembled in a package in order to protect the highly sensitive parts from environmental conditions. This has numerous drawbacks. The first of which is that the multiple interconnected parts must be assembled and placed in the package itself. Thus, known energy scavengers are expensive and difficult to manufacture. What is needed is an energy scavenger which comprises few parts and is thereby cheaper and easier to manufacture.
One fundamental challenge with energy scavengers for kinetic energy is the need for large seismic masses or large diaphragms to reach certain levels of efficiency. A second fundamental challenge for piezoelectric energy scavengers is that the efficiency is directly related to the amount of piezoelectric material that is exposed to resulting high strains. Thus, the efficiency of the scavenger is directly related to the volume and/or area of the device.
There is a need to for an energy scavenger which maximizes the piezoelectric material exposed to high strain while minimizing the complexity of the microelectronic system itself.